Preheat your oven to 375°F (190°C) and lightly grease a 9x9 inch baking dish with butter or non-stick spray.

In a large mixing bowl, combine the chopped rhubarb, granulated sugar, cornstarch, and vanilla extract. Toss well to ensure the rhubarb is evenly coated.

Transfer the rhubarb mixture into the prepared baking dish, spreading it out into an even layer.

In a separate medium bowl, whisk together the flour, oats, shredded coconut, brown sugar, and cinnamon.

Pour the melted butter over the dry topping ingredients. Use a fork or your fingers to mix until the mixture forms moist crumbs.

Evenly sprinkle the coconut crumble over the rhubarb filling in the baking dish.

Bake for 40 to 45 minutes, or until the fruit filling is bubbling and the coconut topping has turned a deep golden brown.

Remove from the oven and let the crunch cool for at least 15-20 minutes before serving to allow the juices to thicken.